There is known an internal combustion engine equipped with a supercharger including actuators that can actively change a supercharging pressure, such as a waste gate valve and a variable nozzle. In intake air quantity control of an internal combustion engine of this type, a target supercharging pressure is determined in accordance with a target air quantity, and a manipulated variable of the actuator is feedback-controlled so that a supercharging pressure measured by a supercharging pressure sensor reaches the target supercharging pressure.
In the above described supercharging pressure feedback control, the supercharging pressure sensor plays an important role in controlling the supercharging pressure with high precision. However, there is no guarantee that the supercharging pressure sensor always functions normally, similarly to the cases of other sensors. Any abnormality such as wire breakage, a short circuit, or deterioration of a sensor element sometimes occurs. Even if feedback control based on the output value of the supercharging sensor is performed in such a case, the actual supercharging pressure cannot be caused to follow the target supercharging pressure. Therefore, in the internal combustion engine equipped with a supercharger that performs supercharging pressure feedback control, a self-diagnosis function of capable of diagnosing abnormality of the supercharging sensor quickly and correctly is required.
As the method for diagnosing abnormality of a supercharging pressure sensor, there is known a method disclosed in Japanese Patent Laid-Open No. 2006-207509, for example. According to the method disclosed in the publication, a difference between a reference supercharging pressure in a predetermined load region of an internal combustion engine and a supercharging pressure obtained by measurement by the supercharging pressure sensor is calculated, and when the difference exceeds a predetermined value, it is determined that abnormality occurs to the supercharging pressure sensor.
However, even if the measured supercharging pressure deviates from a reference supercharging pressure, abnormality of the supercharging pressure sensor is not always the cause thereof. When abnormality occurs to the actuator which is used in supercharging pressure control, the supercharging pressure which is obtained by measurement by the supercharging pressure sensor has the value deviating from the reference supercharging pressure. For example, when the waste gate valve is taken as an example as the actuator, if the waste gate valve does not open due to a malfunction, the supercharging pressure cannot be reduced in accordance with the target. In the case like this, the supercharging pressure measured by the supercharging pressure sensor shows a value higher than the reference supercharging pressure, and therefore, according to the method described in the above described publication, an erroneous diagnosis that abnormality occurs to the supercharging pressure sensor is made.
For this reason, the self-diagnosis function included by the control device for an internal combustion engine equipped with a supercharger is required to be able to diagnose abnormality of the supercharging pressure sensor by distinguishing the abnormality of the supercharging pressure sensor from abnormality of the actuator.
Note that as the prior arts relating to the present invention, the arts described in respective Patent Literatures cited as follows including the art described in the above described publication can be cited. For example, Japanese Patent Laid-Open No. 2007-009877 describes determining abnormality of a waste gate valve by calculating a deviation between the target supercharging pressure and the actual supercharging pressure corresponding to the control duty value each time the control duty value with respect to the waste gate valve is changed by a predetermined amount, and comparing the deviation with an abnormality determination value. However, the technique described in the publication is on the precondition that the supercharging pressure sensor is normal, and is not configured to diagnose abnormality of the waste gate valve by distinguishing the abnormality of the waste gate valve from the abnormality of the supercharging pressure sensor.